Field of the Invention
Embodiments of the invention relate to a solar cell.
Discussion of the Related Art
Recently, as existing energy sources such as petroleum and coal are expected to be depleted, interests in alternative energy sources for replacing the existing energy sources are increasing. Among the alternative energy sources, solar cells have been particularly spotlighted because, as cells for generating electric energy from solar energy, the solar cells are able to draw energy from an abundant source and do not cause environmental pollution.
A solar cell generally includes a substrate and an emitter layer, each of which is formed of a semiconductor, and electrodes respectively formed on the substrate and the emitter layer. The semiconductors forming the substrate and the emitter layer have different conductive types, such as a p-type and an n-type. A p-n junction is formed at an interface between the substrate and the emitter layer.
When light is incident on the solar cell, a plurality of electron-hole pairs are generated in the semiconductor. The electron-hole pairs are separated into electrons and holes by a photovoltaic effect. Thus, the separated electrons move to the n-type semiconductor (e.g., the emitter layer) and the separated holes move to the p-type semiconductor (e.g., the substrate), and then the electrons and holes are collected by the electrodes electrically connected to the emitter layer and the substrate, respectively. The electrodes are connected to each other using electric wires to thereby obtain electric power.
The plurality of electrodes electrically connected to the emitter layer and the substrate collect the electrons and the holes moving to the emitter layer and the substrate and allow the electrons and the holes to move to a load connected to the outside.
However, in this case, because the electrode is formed on the emitter layer on a light incident surface of the substrate as well as a non-incident surface of the substrate, an incident area of light decreases. Hence, efficiency of the solar cell is reduced.
Accordingly, a back contact solar cell, in which all of electrodes collecting electrons and holes are positioned on a rear surface of a substrate, has been developed so as to increase an incident area of light.